Informing the Development of Mobile Apps for HIV Prevention, Treatment and Care: The United States Human Immunodeficiency Virus (HIV) epidemic continues to exact a huge toll, especially among racial and ethnic minorities, and men who have sex with men (MSM). New York City, the setting of our study, has the largest HIV/AIDS epidemic in the nation, making it the ideal setting for the formative research study. The purpose of this study is to conduct formative research to understand the needs, barriers, and facilitators of using mobile phone applications (apps) for HIV prevention, testing, treatment and care. Mobile health technology shows potential as a highly valuable tool in the management and prevention of chronic illnesses such as HIV. The ubiquitous nature of mobile technologies, namely smartphones, in daily life has created opportunities for applications that were not previously possible. Using mobile technologies to more rapidly and accurately assess and modify health-related behavior and biological states can transform patient decision making about their health. Qualitative ethnographic methods and user-centered human-computer interaction research methods will be used to identify the mobile technology needs of users, mobile application (app) design preferences, as well as the barriers and facilitators that prohibit or encourage the uptake and sustained use of mobile apps for HIV prevention. Our sample will include 50 persons living with HIV (PLWH), 25 HIV healthcare providers and 50 high-risk MSM. At each phase of our study, we will use qualitative ethnographic methods and user-centered human-computer interaction research methods to ensure that the app meets the end-user's goals. We will utilize the Information Science Research Framework in which various design processes are employed in order create a design document. The design document will specify the functional requirements for two distinct apps for: 1) meeting the HIV prevention and health care needs of PLWH, including adherence to HIV medications, retention in care, and treatment management, and 2) encouraging HIV testing by identifying testing sites and providing periodic reminders for testing among high- risk MSM. Findings from this study will inform future HIV prevention, testing, treatment and care apps for Smartphones and other new media technologies for HIV prevention and will identify technology preferences and features, HIV-related content requirements, design specifications, and issues related to long-term appeal and maintenance of apps in at-risk or affected populations. Tools developed using this research have the potential to extend the impact and reach of HIV testing programs for high-risk MSM and HIV prevention and health care for PLWH.